refactor(bookspec): the specification lives in its own repository (P13 step 6)

bookspec/ (spec, examples, checker, runner, Lean, GnuCash adapter) moves to
https://git.swaits.com/swaits/bookspec, history kept by git subtree split
(public home; CC BY 4.0 for spec/ and examples/, MIT OR Apache-2.0 for the
code). ledger-core and ledger-package depend on bookspec-checker and
bookspec-runner as git dev-dependencies pinned to
74f2853d5f0db0066147c17fed8033cfe3d83a24, and read the examples through
bookspec_checker::examples(). just check still runs every example via
cargo test --workspace. The pin check against docs/spec/sources and the
rules.md id check move into tests/bookspec.rs (they need this repository's
files). The accounting is unchanged: no example or rule moved.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

plan/served.md

@@ -1717,14 +1717,15 @@ Each unit follows the 8.0.4 template. "A-n" is an owner answer numbered in 8.3.1
 5. **Files:** owns `bookspec/**`; touches `crates/ledger-core/tests/bookspec.rs`, `crates/ledger-package/tests/package.rs`, `docs/spec/rules.md` (ids), `Cargo.toml` (workspace members if the checker joins the workspace).
 6. **Tests and proofs:** `every_bookspec_example_holds` unchanged; `bookspec/checker` tests (the schema, the derivations); `bookspec/lean` builds with standard axioms only.
 7. **Done when:** (1) the checker crate exists and `just check` still checks all 56+ examples; (2) the `Engine` trait and the wanderbooks adapter run the runner green for every claimed rule; (3) every B-rule has an id, statement, source and example; (4) the five laws are theorems in `bookspec/lean`; (5) the GnuCash adapter runs and its differences are settled from the sources (recorded in the As-built block).
-8. **As built:** steps 1-3 landed 2026-10-26 (`579d0eed`); steps 4 and 5 built 2026-10-29 on branch `P13` (step 6 not started: it waits on the owner, see below).
+8. **As built:** steps 1-3 landed 2026-10-26 (`579d0eed`); steps 4 and 5 built 2026-10-29 on branch `P13` and step 6 on 2026-10-29 (the repository of its own, below).
    - **Step 4, the text.** `bookspec/spec/` holds `00-model.md` (definitions, the model, the five laws, how an example is checked) and one file per area (`entry`, `ledger`, `statement`, `period`, `partner`, `asset`, `prepaid`, `revenue`, `arap`, `1099`, `format`), 667 lines of the 3,300 a 60-page edition allows. Every B-rule has a section `### BS-<area>-<n> (B-n)` with status, MUST/SHOULD/MAY statement, sources, symbolic form, examples and applicability; B-39, B-40, B-43, B-45 are reserved sections (allocated, not yet stated in `rules.md`); B-44, stated in `rules.md`, now carries its `bookspec:` line and CONVENTION status (catalogue and index updated). `checker/tests/spec.rs` fails the build on a missing section, a statement without a modal verb, a status that differs from the catalogue, examples that differ from the catalogue, a vendored pin that is not verbatim in its source (whitespace and curly quotes normalized), or more than 60 pages.
    - **The five laws** are Lean theorems `Bookspec.law_debits_equal_credits`, `law_accounting_equation`, `law_trial_balance`, `law_net_income_articulates`, `law_cash_flow_is_change_in_cash` in `bookspec/lean` (Basic, Entry, Statements, Closing, Ledger ported from `verify/lean` under the namespace `Bookspec`; `Laws.lean` states them; `Audit.lean` prints their axioms: `propext`, `Quot.sound`, `Classical.choice` only). `checker/tests/lean.rs` builds and audits when Lean is installed.
    - **New examples (8)**, each figure worked by hand in the file: `entry-an-unbalanced-entry-is-refused`, `entry-a-line-amount-is-positive`, `entry-cents-add-exactly`, `ledger-a-fraction-of-a-cent-is-refused`, `ledger-a-child-account-has-its-parents-type`, `ledger-a-mistake-is-reversed-never-erased`, `statement-the-books-balance-and-the-equation-holds`, `period-a-close-sweeps-the-year-into-capital` (66 in all). Rules now with an example: B-1 to B-12 and B-21, B-23 (`arap-hand-control-posting-refused` also shows it). New refusal words: `unbalanced`, `too_few_lines`, `negative_amount`, `zero_amount`, `finer_than_minor_unit`, `parent_type_mismatch`, `already_reversed`, `period_closed`; a refused entry may carry a non-positive amount. Finding while writing: `close ... to = "retained_earnings"` posts to the role account 3999 Retained Earnings, not to a setup capital account; the example says so.
    - **Step 5, the derivation.** `bookspec/checker/src/derive.rs` is an engine-free reference model (exact decimals) that replays entries, reversals, a close to retained earnings, bills and invoices, derives `trial_balance`, `balances`, `profit_and_loss` and `entry` figures plus the law checks (books net to zero, A = L + E + (R - X)) and checks each refusal against its rule; everything else is reported `Skipped`, never passed. `checker/tests/derive.rs`: no example disagrees; the eight law examples are derived in full; a figure moved by a cent and an unjustified refusal are both caught.
    - **The runner against wanderbooks** (`the_runner_reports_every_claimed_rule_green`) is green for every claimed rule, now including BS-entry-1 to -3, BS-ledger-1 to -6 and -8, BS-statement-1 and -2, BS-period-1 and -2.
    - **GnuCash, the second engine** (`bookspec/gnucash`, ignored tests; needs the `just oracle` image). It claims the rules whose examples ask only for balances. Passes BS-entry-3, BS-ledger-3, BS-statement-1, BS-statement-2. Three differences, settled from the sources and pinned by `gnucash/tests/gnucash.rs`: GnuCash books an unbalanced entry and parks the difference in `Imbalance-USD` (BS-entry-1 refuses it: Pacioli ch. 36, Pub. 583); it reads a credit of minus 100.00 as a debit (BS-entry-2 is a CONVENTION that removes the ambiguity); it rounds 10.005 to 10.01 silently (BS-ledger-1's CHOICE, found by the first cross-check, is not to). The examples stand in each case. GnuCash has no reversal link, so BS-ledger-5, -6 are not claimed by it.
-   - **Not done, and why.** (a) Done when 3 is met for the rules the schema can show; these stated rules still have no example because the schema has no event or query for them: BS-entry-4 (B-28), BS-ledger-7 (B-20), -9 (B-29), -12 (B-44), BS-asset-2 (B-22), -3 (B-24), BS-revenue-1 (B-17), BS-arap-1 (B-18), BS-arap-6 (B-42, whose allocated names `arap-settlement-exact` and `processor-fee-gross-presentation` wait on a payment/settlement event and an aging query), BS-format-1 (B-27); each section says why. B-39, B-40, B-43, B-45 are unstated in `rules.md`. (b) Step 6, the repository of its own, is the owner's call (a public repository, CC BY 4.0 for the text) and waits on step 5 being stable; nothing was pushed. (c) The derivation covers the ledger-core examples; depreciation, schedules, members, 1099s, formats and the cash-flow sections are skipped by the model and checked by the engines only.
+   - **Not done, and why.** (a) Done when 3 is met for the rules the schema can show; these stated rules still have no example because the schema has no event or query for them: BS-entry-4 (B-28), BS-ledger-7 (B-20), -9 (B-29), -12 (B-44), BS-asset-2 (B-22), -3 (B-24), BS-revenue-1 (B-17), BS-arap-1 (B-18), BS-arap-6 (B-42, whose allocated names `arap-settlement-exact` and `processor-fee-gross-presentation` wait on a payment/settlement event and an aging query), BS-format-1 (B-27); each section says why. B-39, B-40, B-43, B-45 are unstated in `rules.md`. (b) Step 6 is done, see the next bullet. (c) The derivation covers the ledger-core examples; depreciation, schedules, members, 1099s, formats and the cash-flow sections are skipped by the model and checked by the engines only.
+   - **Step 6, the repository of its own (D-34, D-65 as amended: Gitea only).** `https://git.swaits.com/swaits/bookspec` is the public home (no GitHub repository, none planned; GitHub's token could not create one and the owner chose Gitea). `git subtree split --prefix=bookspec` kept the history of `bookspec/` (539 commits). The new tree adds `LICENSE-MIT`, `LICENSE-APACHE` (the code), `LICENSE-CC-BY-4.0` (`spec/` and `examples/`), a README licence table, `.github/workflows/check.yml` (fmt, clippy, rustdoc, `cargo test --workspace`; the two Docker-gated GnuCash tests stay ignored) and `repository` metadata. `bookspec_checker::examples()` and `spec_files()` (`include_dir` over the crate's `../examples` and `../spec`) carry the files, so no consumer needs a path. wanderbooks pins `bookspec-checker` and `bookspec-runner` as git dev-dependencies of `ledger-core` (and the checker of `ledger-package`) at `rev = 74f2853d5f0db0066147c17fed8033cfe3d83a24`; `bookspec/` is deleted here, the four `just check` lines for it are gone, and `just check` still runs every example through `cargo test -p ledger-core --test bookspec`. The two checks that read this repository moved here: `every_vendored_pin_is_verbatim` (the pins against `docs/spec/sources`) and `rules_md_carries_every_id` (both in `crates/ledger-core/tests/bookspec.rs`); bookspec keeps the citations' form check. `bookspec/lean` and the GnuCash adapter went with the repository. Raising the pin is a one-line `rev` change in two `Cargo.toml` files.
 
 
 ### 8.3 P4b reference design: receivables and payables, first class (D-45)